Wafers are subjected to various treatments, including chemical treatments in a wide variety of types of reactor. One treatment comprises etching wafers using HF vapour. Because of a wide variety of circumstances, it can be desirable to etch wafers between different deposition treatments. The problem then arises that such an etching substance also has to penetrate into relatively deep wells present in the wafer in order to be able to etch native silicon dioxide. In particular, problems have been detected if a layer of doped oxides deposited using CVD, such as borophosphosilicate glass (BPSG), has to be etched. The methods known in the prior art for etching batches of wafers do not give a uniform result.
This problem increases on increasing the diameter of the wafers. Recently there has been a discernible trend in the market to switch from 200 to 300 mm. If such wafers are etched using conventional techniques, this results in a difference between minimum and maximum etching depth in a range between, for example, 50 .ANG. and 5000 .ANG.. Moreover, it will hardly be possible to remove the native oxides in the mid section of such wafers.
In U.S. Pat. No. 4,798,165, drawn up in the name of ASM International N.V. in Bilthoven, it is proposed, for a reactor in which a single wafer is treated, to supply the gas via a distributor plate arranged above the wafer so that uniform distribution of gas over the wafer is produced. Such a process is satisfactory.